The invention relates to a barrier film which comprises oriented polypropylene. A barrier layer improves moisture barrier properties and reduces oxygen transmission.
Oriented polypropylene films are known for use in packaging operations. U.S. Pat. No. 4,604,324 to Nahmias, et al. discloses multi-layer polypropylene film structure comprising coextruded layers of a base layer of high stereoregularity polypropylene and a skin layer of comparatively low stereoregularity which contains anti-stick additives. In addition, the skin layer can contain up to 10 wt % of a wax to improve heat seal characteristics or optical properties of the film. U.S. Pat. No. 5,254,394 to Bothe, et al., incorporated herein by reference, discloses a polyolefin film for packaging comprising isotactic polypropylene base layer and a top layer of syndiotactic polypropylene which has high sealed-seam strength and excellent optical properties. The layers may contain lubricant additives such as waxes at levels of up to 2 wt %, relative to each layer.
U.S. Pat. No. 5,155,160 to Yeh, et al., incorporated herein by reference, discloses improving barrier properties of crystalline or isotactic polyolefin films by incorporating 3 to 10 wt % wax, such as paraffin wax in the isotactic polyolefin. The reference discloses affecting barrier properties by modifying chill roll conditions.